English abstract
The billion dollar maritime industry is plagued by biofouling leading often to heavy economic penalties. While biocidal paints have been effectively used to reduce biofouling, their associated environmental and toxicology impacts has demonstrated the urgent need of more ecologically acceptable biofouling protection methods. This thesis explores the use of bioinspired zinc oxide (ZnO) nanorods coatings on various substrates which due to photocatalysis produce Reactive Oxygen Species (ROS) preventing biofouling. As a prior investigation, the antifouling (AF) properties of ZnO nanorod (ZnO NR) coated glass substrata were investigated in an out-door mesocosm experiment under natural sunlight. This study demonstrated the effective reduction in density and viability of fouling bacteria and diatoms using ZnO nanorod coating. In the following experiment, AF properties of ZnO NR coated fishing nets were tested and compared with commercial biocidal AF paint during the one month field experiment at Al Mouj marina, Muscat to evaluate their possible application in aquaculture installations. Our results demonstrated that the nanocoated net was significantly better compared to the nets painted with the AF paint in terms of antifouling performance. Metagenomic analysis using Illumina MiSeq sequencing showed that the nanocoated net had similar fouling communities as the control net whereas the nets with AF paint led to the harbouring of harmful organisms. In the next step, ZnO NRs were grown on commercial water filter (polypropylene substrate) and their potential application towards water treatment using solar light was investigated. The results showed that the nanocoated polypropylene substrates have antibacterial and antialgal properties upon photocatalysis and it also prevented regrowth of algae after the photocatalytic treatment. Nanocoated substrate also effectively disinfected natural well water using solar light which suggests that such substrates potentially can be used in water treatment plants. In the last experiment, toxicity of ZnO NRs unsupported and supported on glass substrate, Zno nanoparticles (NPs) and Zn2+ ions was investigated using Artemia salina larvae, Dunaliella salina (alga) and Bacillus cereus (bacteria). The results clearly highlighted the differences of sensitivity of tested organisms towards NPS, NRs and Zn2+ ions. Supported ZnO NRs showed the least toxicity compared to nanoparticles and Zn* ions for all the tested organisms. In conclusion, this study demonstrated that ZnO NRs supported on various substrates can be a good low toxic alternative to modern toxic antifouling methods.
